Revision 1917643

Refine workflow for constructing path-groups.

* tools/hook-scripts/mailer/mailer.py:
  (Config.__init__): _prep_maps() now returns sections that are being
    used to map values. These should be removed from the groups that
    define path-based configuration. Shift that removal here. Also,
    pass the set of path-groups to _prep_groups() rather than dropping
    that off in an instance variable.
  (Config._prep_maps): docco. Change to return a set of the sections
    used for mapping values.
  (Config._prep_groups): take the groups to review, rather than pick
    them up out-of-band via an instance variable.